This invention relates to an electroacoustic amplifier arrangement, comprising a plurality of microphone arrangements, each microphone arrangement comprising a microphone. The microphones of the microphone arrangements being each connectable with an input of amplifier means having an output coupled to a loudspeaker arrangement for triggering at least one loudspeaker associated to the loudspeaker arrangement. A threshold signal generator generates a threshold signal and presents this threshold signal to an output. A microphone arrangement comprising means for coupling or not an output of the associated microphone to the input of the amplifier means dependent upon the presence or absence, respectively, of a control signal. A comparing means has a first input coupled to the output of the microphone, a second input coupled to the output of the threshold signal generator and an output coupled to a control signal input of the coupling means. The comparing means is arranged to compare the microphone signal fed to its first input with the threshold signal fed to its second input and generates the control signal in response to the two signals. The coupling means is arranged to couple the output of the microphone to the input of the amplifier means in the presence of the control signal and to a microphone arrangement to be used in the electroacoustic amplifier arrangement.
The amplifier arrangement of the type mentioned in the opening paragraph is known from GB 2 174 268A and is used, for example, in conference systems. An conferees are located in a conference room in which a sound reproducing system comprising amplifiers and loudspeakers is installed. The conferees each have the disposal of a microphone station which includes a microphone by way of which the conferees' contributions may be reproduced in amplified version in the room by the sound reproducing system. The loudspeakers may be mounted somewhere in the room. Loudspeakers may sometimes be included in the microphone stations. A still further possibility is that the loudspeaker arrangement comprises only loudspeakers included into the microphone stations.
The microphones generally have a so-called voice switch for avoiding, for example, acoustic feedback into the conference room. When a conferee does not speak into his microphone, the microphone is disconnected from the sound reproducing system. When the conferee starts speaking into his microphone, the microphone is connected to the input of the sound reproducing system if there is a sufficiently high microphone signal, so that the conferee's speech is amplified by way of the sound reproducing system. The known microphone arrangement therefore comprises a threshold signal generator means which derives a threshold signal from the signal fed to the loudspeakers. If the microphone signal exceeds this threshold signal, the microphone is coupled to the input of the sound reproducing system.
The prior-art amplifier arrangement, however, has the drawback that microphones are sometimes still connected while the conferee is not speaking. This may lead to the occurrence of acoustic feedback. Another drawback is that in a system in which only a limited number of microphones can be connected, microphones that are activated in the proper fashion indeed, may perhaps not be connected.